After the Russian Conquest of Kazan in the 1550s Opened

After the Russian conquest of Kazan in the 1550s opened the regions of the lower Volga River,

A) few Russians colonized the area because of the lack of cities.
B) the Russians focused mainly on the exploitation of the fur trade.
C) large numbers of Russians colonized the region, but mainly they raised livestock and did little farming.
D) the Russians developed the region for grain cultivation.